The invention relates to a method for placing and igniting a blasting charge for geological tests and to a blasting device for geological tests.
With known methods for preparing for blasting, first of all a shot-hole is drilled, using boring tools, in the ground which is to be tested. Subsequently, an explosives container with an ignition element is lowered into the shot-hole. The shot-hole is then closed and the ignition is triggered. The explosives container has a concentrated spherical or parallelepipedal form in order to realize a centre of explosion that is as punctiform as possible, as is necessary for accurate geological tests. The selected shot-hole diameter must be at least so large that the explosives container passes therethrough and can be lowered effortlessly to the base of the shot-hole. For this purpose, typically shot-hole diameters of 80 mm to 150 mm are required. However, these comparatively large shot-hole diameters have the disadvantage that the shot-holes which are typically 10-30 m deep, involve outlay, are time-consuming and therefore are also costly.
The object of the invention is to provide an improved blasting method and an improved blasting device for geological tests.
The method in accordance with the invention has the initial method steps of drilling a shot-hole in the ground to be tested and hollowing out a blasting space, widened in relation to the shot-hole, at the end of the shot-hole. The shot-hole can be drilled to a comparatively small diameter which need only be dimensioned so that it is of a sufficient size to make the widened blasting space accessible, yet does not have the diameter of the blasting space. Subsequently, an ignition element and a slender explosives container are lowered through the shot-hole into the blasting space and the explosive is forced out of the explosives container into the widened blasting space, where it collects in a concentrated manner in the form of a sphere. Finally, the ignition element is ignited.
Only the blasting space at the lower end of the shot-hole is of a comparatively large width, which is necessary to accommodate the explosive in a concentrated, non bar-shaped form, whilst the selected width of the shot-hole can be just so small to make the blasting space accessible and to load it. To this end, shot-hole diameters of 25 to 60 mm suffice. For the purpose of loading explosives into the widened blasting space through the narrowed shot-hole, the explosive, which is packed in a slender explosives container, together with the ignition element, although so as to be spatially separate from the latter, is lowered through the shot-hole to the blasting space. The diameter of the explosives container is so small that it can be lowered through the shot-hole without any difficulties. When the explosive reaches the blasting space, it is forced out of the slender explosives container and is distributed over the entire width of the blasting space, which is widened in relation to the shot-hole, and is finally ignited. As a result of transporting the explosive to the end of the shot-hole in a slender explosives container that is adapted to the small shot-hole width, the explosive can also be moved through very narrow shot-holes to the shot-hole base. As a result of the fact that the shot-hole diameter is small, drilling can be carried out in a rapid and inexpensive manner and with fewer complications.
The blasting space is preferably hollowed out by introducing a scavenging fluid to the shot-hole end and scavenging out the blasting space with the scavenging fluid that has been introduced. This scavenging-out process can be carried out by injecting compressed air, steam or water. Approximately 80% of geological ground tests are carried out in comparatively soft ground or layers of earth. The comparatively simple manner of widening the lower shot-hole end to form a widened blasting space by scavenging this out with a fluid, for example air, water vapour or water, is a simple and effective method for hollowing out a widened blasting space in comparatively soft ground.
Before the lowering process, an ignition-element holder, holding the ignition element, and the explosives container are preferably coupled together. After the explosive has been forced out into the blasting space, the explosives container is repelled from the ignition-element holder and hauled up out of the bore hole. The ignition-element holder and the explosives container, thus coupled together to form a unit, are lowered through the shot-hole to the blasting space, the explosive is expressed out of the explosives container into the blasting space, the explosives container is separated from the ignition-element holder and the explosives container is finally drawn back out of the shot-hole. On the one hand, on account of the coupling, it becomes easier to lower the explosives container and the ignition-element holder and, on the other hand, as a result of the subsequent separation, the explosives container can be hauled up, re-filled with explosive and used for further blasting.
According to a preferred embodiment of the method, before the ignition element and the explosives container are lowered, a pressure hose is attached to the explosives container and, after the lowering process, the explosive is forced out of the container as a result of applying pressure to the explosives container through the pressure hose. Thus, a non-electrical method is provided for expressing the explosive out of the explosives container, which method does not entail any additional risks of unintentional premature ignition and operates in a very reliable manner. An alternative solution is the use of a push rod for mechanically forcing out the explosive.
The explosives container is preferably pushed off as a result of applying pressure through the pressure hose to a detachable coupling between the explosives container and the ignition portion. The action of pushing off or uncoupling the explosives container from the ignition-element holder by applying pressure, for example by means of compressed air, does not hold any additional risks of an explosion being triggered unintentionally, can be realized in a simple manner mechanically and is highly reliable.
The blasting device in accordance with the invention for geological tests in accordance with claim 6 has an explosives container with free-flowing explosive, which explosives container can be lowered in a shot-hole in a suspended manner, a device for forcing the explosive out of the explosives container, an ignition-element holder arranged on the explosives container with an ignition element for igniting the explosive which has been forced out, and a flow path through which the explosive, which has been forced out, can flow from the explosives container to the ignition element. The explosive is transported in a transport container as far as the actual blasting location, for example as far as the base of the shot-hole, and only there is forced out of the explosives container. The cross section of the explosives container and the cross section of the ignition-element holder are adapted to the shot-hole diameter so that explosive can also be transported through narrow shot-holes in a complete and reliable manner as far as the end of the shot-hole. In this way, shot-holes that have comparatively small diameters suffice, whereby the costs of drilling and the time spent drilling the shot-hole are in turn reduced. The explosive first reaches the blasting location whilst in contact with the ignition element. Unintentional triggering of an explosion, before the explosive has reached the base of the shot-hole, is thereby precluded, whereby the handling thereof becomes safer.
According to a preferred embodiment, the ignition-element holder is arranged axially in front of the explosives container, with the explosive being forced out of the explosives container through the substantially axial flow path in the direction of the ignition element. In this way, it is possible to realize a very slender construction, for the explosives container and ignition-element holder. The explosive, which is expressed out of the explosives container, runs downwards out of the explosives container and surrounds the ignition-element holder, arranged below the explosives container, and the ignition element respectively. As a result of this arrangement, the overall construction that is realized is slender and it is guaranteed that the explosive is reliably forced out in the direction of the ignition element.
The explosives container preferably has a pushing off device for pushing the detachable explosives container off from the ignition-element holder. After the explosive has been forced out, the explosives container can be pushed off from the ignition-element holder remaining in the bore hole and can be drawn back out of the bore hole. The explosives container can subsequently be refilled with explosive and can be reused.
According to a preferred embodiment, the explosives container is an elongated cylinder body and the forcing out device is a plunger which can be moved in a longitudinal direction in the cylinder body. The plunger-cylinder arrangement represents a construction of the explosives container with a forcing out device that is slender and at the same time functions in a reliable manner.
According to a preferred embodiment, the explosives container has a pressure-hose connection through which pressure can be applied to the rear side of the plunger that is remote from the explosive. A pressure hose, for example an air-pressure hose, is connected to the pressure-hose connection before the explosives container is lowered. As soon as the explosives container has been lowered and has reached the base of the shot-hole, pressure is applied to the plunger by way of the pressure hose so that the plunger forces the explosive out of the explosives container. As a result of the use of compressed air to drive the plunger or differently designed forcing out devices, no additional risk of explosion arises. The compressed-air drive of the plunger can be realized in a reliable and inexpensive manner.
The ignition-element holder preferably has a protective pocket, which surrounds the ignition element, for the purpose of accommodating the explosive which is forced out. In this way, the explosive remains concentrated in the form of a sphere about the ignition element and cannot seep away in the ground. At the same time, the protective pocket protects the ignition element when the ignition-element holder is lowered and subsequently protects the explosive, which is forced out, from contamination, moisture and water from outside.
According to a preferred embodiment, the plunger forms the pushing off device, with the plunger and the explosives container being designed in a such a way that at the end of its forcing out travel the plunger pushes the ignition-element holder off from the explosives container. The plunger is thus used both to express the explosive out of the cylinder and alsoxe2x80x94at the end of its plunger strokexe2x80x94as a pushing off device to push the emptied explosives container off from the ignition-element holder. A simple construction and design of a pushing off device are thus realized.
As an alternative to this, the pushing off device can also be formed by a fluid duct on the explosives container, in which case the fluid duct ends at a stop face of the ignition-element holder and pressure can be applied by way of the pressure-hose connection to push off the ignition-element holder. This can be effected, for example, by first opening up the fluid duct at the end of the plunger stroke, whereupon pressure from the pressure hose or pressure-hose connection is applied to the fluid duct. The pressure acts through the fluid duct on the stop face of the ignition-element holder, whereby the explosives container is pushed back or pushed off the ignition-element holder. With this construction as well, a simple pushing off device is provided that uses the pressure-hose connection as an energy source.